1. Field of the Invention
The present invention relates generally to communications networks and, more particularly, to an apparatus and method for dynamically allocating resources within such networks to achieve increased efficiency in resource utilization.
2. Description of the Related Art
A communications network supplies a communication path between two or more end users and typically has the capacity to connect only a finite amount of communication traffic at any given instant. Each call consumes some portion of the total available communication resources. In this regard, it will be observed that there are two primary communication resources to be employed in any communication system, namely, average transmitted power and channel bandwidth.
The average transmitted power is the average power of the transmitted signal. The channel bandwidth defines the range of frequencies that the channel can handle for the transmission of signals with satisfactory fidelity. A general system design objective is to use these two resources as efficiently as possible. In most systems, one resource may be considered more important than the other. Hence, we may also classify communication channels as power-limited or band-limited. For example, the telephone circuit is a typical band-limited channel, whereas a deep-space communication link or a satellite channel is typically power-limited.
The transmitted power is important because, for a receiver of prescribed noise figure, it determines the allowable separation between the transmitter and receiver. In other words, for a receiver of prescribed noise figure and a prescribed distance between it and the transmitter, the available transmitted power determines the signal-to-noise ratio at the receiver input. This, subsequently, determines the noise performance of the receiver. Unless performance exceeds a certain design level, the transmission of message signals over the channel is not considered to be satisfactory. Additionally, channel bandwidth is important because, for a prescribed band of frequencies characterizing a message signal, the channel bandwidth determines the number of such message signals that can be multiplexed over the channel. In other words, for a prescribed number of independent message signals that have to share a common channel, the channel bandwidth determines the band of frequencies that may be allotted to the transmission of each message signal without discernible distortion.
In any event, as utilized herein, the term "resource" should be understood as being inclusive of, but not limited to, an RF channel (e.g. a set of frequencies or time slots as in Frequency Division Multiple Access--FDMA, Time Division Multiple Access--TDMA, and hybrids thereof), a code associated with a user for the purposes of facilitating communication (as is utilized, for example, in a Direct Sequence Code Division Multiple Access system--CDMA), and a hopping sequence (i.e., an ordinal list specifying the order in which a given set of entities, a set of frequencies, for example, may be accessed in succession for the purposes of communication), as is employed in a Frequency Hopped Spread Spectrum (FHSS) scheme.
A network may be viewed as having a number of base stations. Each base station receives communications from several input ports and distributes these communications among several output ports. The end parties to a call communicate directly with their respective base stations. In some cases, the calling and called parties utilize the same network base station. However, in other cases communication paths are established between diverse base stations, perhaps through intermediary base stations.
When a communications network is configured to accommodate mobile end users, the need to conserve network resources increases. The service area is partitioned into connected service domains known as cells. Within a particular cell, radiotelephone users communicate via radio links with a base station (BS) serving that cell, the base station being connected to other base stations of the radio network. To communicate using this radio network, each user is assigned one of a discrete set of channels. When mobile end users are involved, RF links are typically used to communicate with the end users. These RF links represent scarce resources which must be conserved to the maximum extent possible. Since the end users are mobile, the locations of called parties cannot be determined simply by examining data describing the called parties' identities. Hence, additional network resources must be consumed and additional intelligence must be designed into the network to determine how to service a "roaming" subscriber whose location varies.
The conservation of network resources becomes especially difficult in a network where at least some of the base stations of the network are themselves mobile. This situation may occur, for example, when satellites in moving orbits are used as network base stations. In this situation, the selection of particular network base stations to use in establishing communication paths depends upon which satellites are in convenient locations at the instant a communication is delivered. Moreover, the communication path definitions change from instant to instant as the satellites travel in their orbits. This instant-to-instant change can simultaneously affect thousands or even millions of communication paths through the network. The network resources needed to coordinate the instant-to-instant changes for a multitude of communication paths can potentially be great enough to make operation of the network impractical.
In the context of wireless, terrestrial-based FDMA/TDMA communication systems, Fixed Channel Allocation (FCA) is presently used to obtain access to the channels in the cells in substantially all systems deployed around the world. With FCA, a fixed set of channels are assigned to each cell. Specifically, efficient use of available resources is attempted by designating co-user cells that are sufficiently separated spatially so that the combined interference generated by all co-user cells, as well as other types of system interference (such as adjacent channel interference) is below tolerable levels. By allowing wider access to channels, trunking efficiencies may be realized, thereby reducing the idle time of channels. Such fixed partitioning of resources is not optimal, however, because a cell is precluded from using resources not initially assigned to it even when such use would not cause a violation of operational constraints. As such, FCA is rigid and not adaptable to satisfying a volatile, shifting channel demand. As the number of subscribers to cellular and personal telecommunication networks increases, the channel demand profile can experience rapid changes. The rigid nature of FCA can be a serious obstacle to providing a communication channel to a mobile user at the time it is needed. Thus, current frequency planning and network control are rapidly becoming impractical and burdensome.
One possible solution to the network management problems created by increased call volume is Dynamic Channel Allocation (DCA) where each channel is available for use in every cell. Unlike FCA, DCA adapts to local interference and traffic conditions. However, channel quality can be impaired by a channel in a nearby cell and/or a weak signal strength, and a channel quality level which is below threshold will prevent a channel from being immediately accessed by an incoming user.
It is therefore an object of the present invention to optimally utilize an available resource, such as the RF spectrum, by providing a scheme which is capable of dynamically allocating resources among the cells of a communication network while respecting the operational constraints thereof.